Refrigerator appliance and method of operating a refrigerator appliance

ABSTRACT

The present invention provides a refrigerator appliance and for operation of a refrigerator appliance. The refrigerator appliance and method of operating a refrigerator appliance include features for regulating the time between evaporator defrost cycles to efficiently defrost the evaporator. Features are also included for increasing the temperature of refrigerant circulating through a refrigeration system of the refrigerator appliance to prevent condensation on outer surfaces of the refrigerator.

FIELD OF THE INVENTION

The subject matter of the present disclosure relates generally to methods and systems for regulating the time between evaporator defrost cycles and increasing the temperature of the refrigerant to prevent condensation on external surfaces of the refrigerator appliance.

BACKGROUND OF THE INVENTION

Generally, refrigerator appliances include a cabinet that defines a fresh food chamber for receipt of food items for storage. Many refrigerator appliances further include one or more freezer chambers for receipt of food items for freezing and storage. Various mullions typically divide the various chambers. For example, a mullion can be disposed between the fresh food chamber and freezer chamber. In “french door” style refrigerator appliances, an articulating mullion can be mounted to one of the fresh food chamber doors and positioned between the fresh food chamber doors when closed.

One problem frequently encountered with modern refrigerators is condensation on the outside of the cabinet or other surfaces of the refrigerator, such as the mullions. Condensation occurs when a surface is at a temperature below the dew point temperature of the surrounding air. Once air contacts such surface, moisture in the air will condense on the surface. As such condensation accumulates, it may be unsightly and may eventually drip or run onto the floor.

Various attempts to reduce such condensation have been made. For example, electric heaters have been embedded in the various components, such as the mullions, to heat the mullions and reduce condensation. However, the use of such heaters increases the energy use of the associated refrigerator appliance. Additionally, such electric heaters and associated components, such as humidity sensors, can increase the cost and the complexity of wiring of the associated refrigerator appliance. Therefore, other methods of increasing the temperature of the refrigerator surfaces, such as increasing the temperature of refrigerant circulating in proximity to such surfaces, could be more cost and energy efficient.

Another problem encountered with modern refrigerators is inefficient defrosting of the evaporator of the refrigeration system. For example, when the evaporator is off, frost can accumulate on the evaporator and thereby reduce the efficiency of the evaporator. One effort to reduce or eliminate frost has been to utilize a heater, such as an electric heater, to heat the evaporator when the evaporator is not operating, with a set period of time elapsing between applications of heat. However, different environmental and use conditions of the refrigerator can cause different amounts of frost to accumulate on the evaporator during the set period of time. Therefore, applying heat only at set intervals such that heat must be applied for different intervals of time is an inefficient use of the heater and may increase the energy consumption of the system and/or increase the wear on the refrigeration components.

Accordingly, improved refrigerator appliances are desired. In particular, a refrigerator appliance with features for regulating the time between evaporator defrost cycles and increasing the temperature of the refrigerant to prevent condensation would be advantageous. Additionally, a method of operating a refrigerator appliance to regulate the time between evaporator defrost cycles and to increase the temperature of the refrigerant to prevent condensation would be beneficial.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a refrigerator appliance and for operation of a refrigerator appliance. The refrigerator appliance and method of operating a refrigerator appliance include features for regulating the time between evaporator defrost cycles to efficiently defrost the evaporator. Features are also included for increasing the temperature of refrigerant circulating through a refrigeration system of the refrigerator appliance to prevent condensation on outer surfaces of the refrigerator. Additional aspects and advantages of the invention will be set forth in part in the following description, may be apparent from the description, or may be learned through practice of the invention.

In a first exemplary embodiment, a method for operating a refrigerator appliance is provided. The refrigerator appliance comprises a refrigeration system for cycling a refrigerant therethrough that includes a compressor, a condenser, and an evaporator. The method includes the steps of activating a defrost heater configured to melt ice built up on the evaporator; counting a time t_(defrost); determining if evaporator is defrosted and, if so, then deactivating the defrost heater; determining whether to increase the refrigerant temperature to prevent condensation on the external surfaces of the refrigerator appliance and, if so, then decreasing a condenser fan speed.

In a second exemplary embodiment, a method for operating a refrigerator appliance is provided. The refrigerator appliance comprising a refrigeration system for cycling a refrigerant therethrough that includes a compressor, a condenser, and an evaporator. The method includes the steps of activating a defrost heater configured to melt ice built up on the evaporator; counting a time t_(defrost); determining if evaporator is defrosted and, if so, then deactivating the defrost heater; determining whether to increase the refrigerant temperature to prevent condensation on the external surfaces of the refrigerator appliance and, if so, then increasing the compressor speed.

In a third exemplary embodiment, a refrigerator appliance is provided. The refrigerator appliance includes at least one compartment for storing food items and a refrigeration system for cycling a refrigerant therethrough that includes a compressor, a condenser, a condenser fan, an evaporator, and a defrost heater configured to melt ice accumulated on the evaporator. The refrigerator appliance also includes a controller in operative communication with the compressor and the condenser fan. The controller is configured for activating a defrost heater configured to melt ice built up on the evaporator; counting a time t_(defrost); determining if evaporator is defrosted and, if so, then deactivating the defrost heater; determining whether to increase the refrigerant temperature to prevent condensation on the external surfaces of the refrigerator appliance and, if so, then decreasing a condenser fan speed.

These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 provides a front view of a refrigerator appliance according to an exemplary embodiment of the present subject matter.

FIG. 2 provides a schematic view of a refrigeration system of the exemplary refrigerator appliance of FIG. 1.

FIG. 3 provides a chart illustrating an exemplary method for operating a refrigerator appliance according to the present subject matter.

FIG. 4 provides a graph of the mass of accumulated ice on the evaporator and the time interval between defrost cycles as a function of defrost time according to an exemplary embodiment of the present subject matter.

FIG. 5 provides an exemplary time-moisture curve according to one embodiment of the present subject matter.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

FIG. 1 provides a front view of a representative refrigerator appliance 10 in an exemplary embodiment of the present invention. More specifically, for illustrative purposes, the present invention is described with a refrigerator appliance 10 having a construction as shown and described further below. As used herein, a refrigerator appliance includes appliances such as a refrigerator/freezer combination, side-by-side, bottom mount, compact, and any other style or model of a refrigerator appliance. Accordingly, other configurations including multiple and different styled compartments could be used with refrigerator appliance 10, it being understood that the configuration shown in FIG. 1 is by way of example only.

Refrigerator appliance 10 includes a fresh food storage compartment 12 and a freezer storage compartment 14. Freezer compartment 14 and fresh food compartment 12 are arranged side-by-side within an outer case 16 and defined by inner liners 18 and 20 therein. A space between case 16 and liners 18 and 20, and between liners 18 and 20, is filled with foamed-in-place insulation. Outer case 16 normally is formed by folding a sheet of a suitable material, such as pre-painted steel, into an inverted U-shape to form the top and side walls of case 16. A bottom wall of case 16 normally is formed separately and attached to the case side walls and to a bottom frame that provides support for refrigerator appliance 10. Inner liners 18 and 20 are molded from a suitable plastic material to form freezer compartment 14 and fresh food compartment 12, respectively. Alternatively, liners 18, 20 may be formed by bending and welding a sheet of a suitable metal, such as steel.

A breaker strip 22 extends between a case front flange and outer front edges of liners 18, 20. Breaker strip 22 is formed from a suitable resilient material, such as an extruded acrylo-butadiene-styrene based material (commonly referred to as ABS). The insulation in the space between liners 18, 20 is covered by another strip of suitable resilient material, which also commonly is referred to as a mullion 24. In one embodiment, mullion 24 is formed of an extruded ABS material. Breaker strip 22 and mullion 24 form a front face, and extend completely around inner peripheral edges of case 16 and vertically between liners 18, 20. Mullion 24, insulation between compartments, and a spaced wall of liners separating compartments, sometimes are collectively referred to herein as a center mullion wall 26. In addition, refrigerator appliance 10 includes shelves 28 and slide-out storage drawers 30, sometimes referred to as storage pans, which normally are provided in fresh food compartment 12 to support items being stored therein.

Refrigerator appliance 10 can be operated by one or more controllers 11 or other processing devices according to programming and/or user preference via manipulation of a control interface 32 mounted, e.g., in an upper region of fresh food storage compartment 12 and connected with controller 11. Controller 11 may include one or more memory devices and one or more microprocessors, such as a general or special purpose microprocessor operable to execute programming instructions or micro-control code associated with the operation of the refrigerator appliance. The memory may represent random access memory such as DRAM, or read only memory such as ROM or FLASH. In one embodiment, the processor executes programming instructions stored in memory. The memory may be a separate component from the processor or may be included onboard within the processor. Controller 11 may include one or more proportional-integral (“PI”) controllers programmed, equipped, or configured to operate the refrigerator appliance according to exemplary aspects of the control methods set forth herein. Accordingly, as used herein, “controller” includes the singular and plural forms.

Controller 11 may be positioned in a variety of locations throughout refrigerator appliance 10. In the illustrated embodiment, controller 11 may be located e.g., behind an interface panel 32 or doors 42 or 44. Input/output (“I/O”) signals may be routed between the control system and various operational components of refrigerator appliance 10 along wiring harnesses that may be routed through e.g., the back, sides, or mullion 26. Typically, through user interface panel 32, a user may select various operational features and modes and monitor the operation of refrigerator appliance 10. In one embodiment, the user interface panel may represent a general purpose I/O (“GPIO”) device or functional block. In one embodiment, the user interface panel 32 may include input components, such as one or more of a variety of electrical, mechanical or electro-mechanical input devices including rotary dials, push buttons, and touch pads. The user interface panel 32 may include a display component, such as a digital or analog display device designed to provide operational feedback to a user. User interface panel 32 may be in communication with controller 11 via one or more signal lines or shared communication busses.

In one exemplary embodiment of the present invention, one or more temperature sensors are provided to measure the temperature in the fresh food compartment 12 and the temperature in the freezer compartment 14. For example, first temperature sensor 52 may be disposed in the fresh food compartment 12 and may measure the temperature in the fresh food compartment 12. Second temperature sensor 54 may be disposed in the freezer compartment 14 and may measure the temperature in the freezer compartment 14. This temperature information can be provided, e.g., to controller 11 for use in operating refrigerator 10 as will be more fully discussed below. These temperature measurements may be taken intermittently or continuously during operation of the appliance and/or execution of a control system as further described below.

A shelf 34 and wire baskets 36 are also provided in freezer compartment 14. In addition, an ice maker 38 may be provided in freezer compartment 14. A freezer door 42 and a fresh food door 44 close access openings to freezer and fresh food compartments 14, 12, respectively. Each door 42, 44 is mounted to rotate about its outer vertical edge between an open position, as shown in FIG. 1, and a closed position (not shown) closing the associated storage compartment. In alternative embodiments, one or both doors 42, 44 may be slidable or otherwise movable between open and closed positions. Freezer door 42 includes a plurality of storage shelves 46, and fresh food door 44 includes a plurality of storage shelves 48.

Referring now to FIG. 2, refrigerator appliance 10 may include a refrigeration system 200. In general, refrigeration system 200 is charged with a refrigerant that is flowed through various components and facilitates cooling of the fresh food compartment 12 and the freezer compartment 14. For example, refrigeration system 200 may include a compressor 202 for compressing the refrigerant, as is generally understood, thus raising the temperature and pressure of the refrigerant. Compressor 202 may for example be a variable speed compressor, such that the speed of the compressor 202 can be varied between zero and 100 percent by controller 11. Refrigeration system 200 may further include a condenser 204, which may be disposed downstream (in the direction of flow of the refrigerant) of the compressor 202. Thus, condenser 204 may receive refrigerant from the compressor 202, and may condense the refrigerant, as is generally understood, by lowering the temperature of the refrigerant flowing therethrough due to, e.g., heat exchange with ambient air. A condenser fan 206 may be used to force air over condenser 204 as illustrated to facilitate heat exchange between the refrigerant and the surrounding air. Condenser fan 206 can be a variable speed fan—meaning the speed of condenser fan 206 may be controlled or set anywhere between and including, e.g., 0 and 100 percent. The speed of condenser fan 206 can be determined by, and communicated to, fan 206 by controller 11.

Refrigeration system 200 may further include an evaporator 210 disposed downstream of the condenser 204. Alternatively, it should be noted that condensation of the refrigerant may occur in some refrigeration systems 200 without a condenser 204, such as in suitably configured conduits extending between compressor 202 and evaporator 210. Additionally, an expansion device 208 may be utilized to expand the refrigerant, thus further reduce the pressure of the refrigerant, leaving condenser 204 before being flowed to evaporator 210. Evaporator 210 generally is a heat exchanger that transfers heat from air passing over the evaporator 210 to refrigerant flowing through evaporator 210, thereby cooling the air and causing the refrigerant to vaporize. An evaporator fan 212 may be used to force air over evaporator 210 as illustrated. As such, cooled air is produced and supplied to refrigerated compartments 12, 14 of refrigerator appliance 10. In one exemplary embodiment of the present invention, evaporator fan 212 can be a variable speed evaporator fan—meaning the speed of fan 212 may be controlled or set anywhere between and including, e.g., 0 and 100 percent. The speed of evaporator fan 212 can be determined by, and communicated to, evaporator fan 212 by controller 11.

Evaporator 210 may be in communication with fresh food compartment 12 and freezer compartment 14 to provide cooled air to compartments 12, 14. Alternatively, refrigerator loop 200 may include more two or more evaporators, such that at least one evaporator provides cooled air to fresh food compartment 12 and at least one evaporator provides cooled air to freezer compartment 14. In other embodiments, evaporator 210 may be in communication with any suitable component of the refrigerator appliance 10. For example, in some embodiments, evaporator 210 may be in communication with ice maker 38, such as with an ice compartment of the ice maker 38. From evaporator 210, refrigerant may flow back to and through compressor 202, which may be downstream of evaporator 210, thus completing a closed refrigeration loop or cycle.

As shown in FIG. 2, a defrost heater 214 may be utilized to defrost evaporator 210, i.e., to melt ice that accumulates on evaporator 210. Heater 214 may be activated periodically; that is, a period of time t_(ice) elapses between when heater 214 is deactivated and when heater 214 is reactivated to melt a new accumulation of ice on evaporator 210. The period of time t_(ice) may be a preprogrammed period such that time t_(ice) is the same between each period of activation of heater 214, or the period of time may vary, as will be further described below. Alternatively, heater 214 may be activated based on some other condition, such as the temperature of evaporator 210 or any other appropriate condition.

Additionally, a defrost termination thermostat 216 may be used to monitor the temperature of evaporator 210 such that defrost heater 214 is deactivated when thermostat 216 measures that the temperature of evaporator 210 is above freezing, i.e., greater than 32° F. In some embodiments, thermostat 216 may send a signal to controller 11 or other suitable device to deactivate heater 214 when evaporator 210 is above freezing. In other embodiments, defrost termination thermostat 216 may comprise a switch such that heater 214 is switched off when thermostat 216 measures that the temperature of evaporator 210 is above freezing.

As further shown in FIG. 2, refrigeration system 200 may also include a loop 100 that may be routed through portions of refrigerator appliance 10. For example, referring back to FIG. 1, a portion of loop 100 may be positioned adjacent mullion 24. Loop 100 contains refrigerant that has been heated from being pressurized by compressor 202 and, thus, is at a higher temperature than the ambient air and/or casing of refrigerator 10. Accordingly, as the refrigerant circulates about loop 100, heat is released and is available for exchange with air and/or components in contact with loop 100. By selecting a particular routing for loop 100 within refrigerator 10, i.e., between outer case 16 and inner liners 18, 20, this heat may be made available at various locations in the refrigerator as needed for the heating of outer surfaces such as mullion 24 to prevent the formation of condensation on such surfaces.

Referring now to FIG. 3, an exemplary method for operating refrigerator appliance 10 is illustrated, which may be performed in whole or in part by controller 11 or any other suitable device or devices. At step 302, defrost heater 214 is activated to melt ice built up on evaporator 210. At step 304, controller 11 begins counting time t_(defrost), which is the time required to melt the ice built up on evaporator 210. Next, controller 11 determines at step 306 whether evaporator 210 has been defrosted. As described, controller 11 may determine whether evaporator 210 has been defrosted by monitoring defrost termination thermostat 216, which may indicate that evaporator 210 is defrosted when the measured temperature of evaporator 210 is greater than freezing. If evaporator 210 is not defrosted, controller 11 continues to count time t_(defrost) and to determine whether evaporator 210 has been defrosted. However, if at step 306 evaporator 210 has been defrosted, defrost heater 214 is deactivated at step 308 and controller 11 stops counting time t_(defrost).

Using time t_(defrost), controller 11 can regulate the defrost cycle and adjust the refrigerant temperature to prevent excessive ice buildup on evaporator 210 and to prevent condensation from forming on external surfaces of refrigerator appliance 10. At step 310 of method 300, time interval t_(ice) is established. As discussed, defrost heater 214 may be activated periodically such that a period of time t_(ice) elapses between when heater 214 is deactivated and when heater 214 is reactivated. Time t_(ice) may be established based on the time t_(defrost) that was required to defrost the evaporator.

In some embodiments, a correlation between time t_(defrost) and time t_(ice) may be determined experimentally, e.g., prior to or during the manufacture of refrigerator appliance 10, and plotted as a defrost curve that is programmed into controller 11. As shown in the exemplary correlation of FIG. 4, the time t_(defrost) required to defrost evaporator 210 is proportional to the mass of the ice that has built up on evaporator 210; that is, a longer time t_(defrost) is required to melt more ice. As time t_(defrost) increases, time t_(ice) between defrost cycles may be decreased because a larger time t_(defrost) indicates the environmental and use conditions are such that more ice is likely to accumulate on evaporator 210, as further described below. Thus, evaporator 210 should be defrosted more often (time t_(ice) should be shorter) such that the operation of evaporator 210 is not hindered by the accumulation of ice. How much shorter t_(ice) should be can be determined by trial and error until optimal values, i.e., the values of t_(ice) that best preserve the efficiency of evaporator 210, are found. That is, different values of t_(ice) may be used for a given time t_(defrost) until an optimal value of t_(ice) is determined. The optimal values for a range of times t_(defrost) may then be plotted as shown in FIG. 4 and programmed into controller 11. Alternatively, one or more equations may be derived from the correlation and programmed into controller 11. Then, using either the curve or one or more equations derived from the correlation, controller 11 may establish time t_(ice) for the measured time t_(defrost).

As discussed and as shown in FIG. 4, the time t_(defrost) required to defrost evaporator 210 is proportional to the mass of the ice that has built up on evaporator 210. Thus, the mass of ice accumulated on evaporator 210 may be determined based on time t_(defrost) for different environmental and use conditions. Further, experimental data for the time t_(defrost) required to defrost evaporator 210 following a certain number of door openings at a certain humidity may be used to generate one or more time-moisture curves, as shown in FIG. 5. For example, in an exemplary experiment performed, e.g., prior to or during the manufacture of refrigerator appliance 10, the environmental absolute humidity may be regulated to 0.04 lb_(H2O)/lb_(air) and following 45 openings of refrigerator doors 42, 44, a defrost cycle may be initiated and t_(defrost) may be measured. These measurements may be repeated for a range of absolute humidity and door opening values, and then the data may be plotted to generate one or more curves, such as the curve shown in FIG. 5. Alternatively, one or more transfer functions may be derived from the data. These curves and/or transfer functions may be programmed into controller 11 during the manufacture of refrigerator 10 such that controller 11 can regulate the operation of refrigerator 10, as describe, without requiring, e.g., components to measure the humidity or the number of openings of doors 42, 44.

Using time-moisture curves or functions, the relative magnitude of time t_(defrost) may be ascertained, which can indicate the environmental and use conditions experienced by refrigerator 10. That is, for a given time t_(defrost), controller 11 may determine whether the time t_(defrost) is greater or less than the previous time t_(defrost) and how the time t_(defrost) compares to the minimum and maximum times t_(defrost) (e.g., whether the time t_(defrost) is almost equal to the minimum or maximum value or whether the time t_(defrost) is closer to either the minimum and maximum values). The relative magnitude of time t_(defrost) may indicate whether doors 42, 44 were opened more or less frequently or the humidity increased or decreased following the previous defrost cycle. Other methods of determining the relative magnitude of time t_(defrost) and/or the mass of ice accumulated on evaporator 210 may also be used.

Because defrost heater 214 must be activated longer to melt a larger mass of ice, a larger value for time t_(defrost) indicates more ice accumulated on evaporator 210 from, e.g., higher humidity and/or more frequent opening of refrigerator doors 42, 44. Likewise, if time t_(defrost) is a smaller value, then less ice accumulated on evaporator 210. To avoid a larger time t_(defrost) when defrost heater 214 is next activated (i.e., to shorten the next defrost cycle), controller 11 may determine that time interval t_(ice) should be shortened from the previous time interval t_(ice). Accordingly, following a relatively longer defrost cycle (when time t_(defrost) is relatively large), the time t_(ice) to the next defrost cycle may be shorter. Then, if the time t_(defrost) of the next defrost cycle is shorter, the next time interval t_(ice) may be lengthened. In this way, the defrost cycles of refrigerator appliance 10 can be adapted to the environmental and use conditions of the appliance optimize the defrosting of evaporator 210, which can provide benefits such as energy savings and reducing wear on the refrigeration components.

After establishing time t_(ice), at step 312 controller 11 determines whether to increase the temperature of the refrigerant flowing through refrigeration system 200 to prevent condensation from forming on such surfaces. Controller 11 may use time t_(defrost) to determine whether to increase the temperature of the refrigerant. Given the time that was required to defrost the evaporator and the frequency of door openings, controller 11 will select the outside absolute humidity from the one or more programmed time-moisture curves to determine, at various temperatures, the rate of condensation on the exterior of the case 16 and/or other components of refrigerator 10. As discussed, if a larger time t_(defrost) is required to melt the ice accumulated on evaporator 210, refrigerator appliance 10 may be operating in a higher humidity environment and/or refrigerator doors 42, 44 may have been opened more often, which causes more ice to accumulate on evaporator 210. In addition to increasing the mass of ice that builds up on evaporator 210, higher humidity may cause condensation to form on the outer surfaces of refrigerator appliance 10, such as, e.g., breaker strip 22 and mullion 24, if the outer surfaces are too cool. Accordingly, if time t_(defrost) is sufficiently large, e.g., when compared to a time-moisture curve or used in a transfer function as described, controller 11 may determine that the refrigerant temperature should be increased, and method 300 proceeds to step 314. However, if at step 312 controller 11 determines the temperature of the refrigerant should not be increased, method 300 proceeds to step 316, described below.

To reduce condensation on the outer surfaces, the temperature of the outer surfaces may be raised by increasing the temperature of the refrigerant flowing through refrigeration system 200 may be increased. As discussed, refrigeration system 200 may include loop 100 positioned adjacent the outer surfaces of refrigerator appliance 10 to heat such surfaces. Thus, increasing the temperature of the refrigerant circulating through loop 100 will increase the temperature of the outer surfaces.

The refrigerant temperature may be increased in several ways. For example, the speed of condenser fan 206 may be decreased to slow the rate of heat exchange between the refrigerant and ambient air as the refrigerant circulates through condenser 204. In this way, the temperature of the refrigerant will not be as greatly reduced as the refrigerant passes through condenser 204. As a further example, the speed of compressor 202 may be increased, thereby increasing the pressure and the temperature of the refrigerant as it passes through compressor 202 more than if compressor 202 was operated at a lower speed. In some embodiments, both the condenser fan speed and the compressor speed may be modulated to increase the temperature of the refrigerant flowing through refrigeration system 200. Therefore, at step 314, controller 11 may decrease the speed of condenser fan 206, increase the speed of compressor 202, or both. As appropriate, controller 11 may also regulate other components of refrigeration system 200 to increase the temperature of the refrigerant. For example, the evaporator fan speed may be increased to increase the mass flow through the compressor and the condenser, thus raising the pressure and temperature of the refrigerant flowing through the condenser. As a further example, electric heaters may also be provided for heating the external surfaces of refrigerator appliance 10, and such heaters may be modulated to regulate moisture condensation and accumulation on external surfaces such as, e.g., breaker strip 22 and mullion 24.

After the condenser fan and/or compressor speeds are modulated to increase the refrigerant temperature, or if the refrigerant temperature does not need to be increased, controller 11 waits time interval t_(ice), as established at step 310, before returning to step 302 and reactivating defrost heater 214.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. 

What is claimed is:
 1. A method for operating a refrigerator appliance, the refrigerator appliance comprising a refrigeration system for cycling a refrigerant therethrough that includes a compressor, a condenser, and an evaporator, the method comprising the steps of: activating a defrost heater configured to melt ice built up on the evaporator; counting a time t_(defrost); determining if evaporator is defrosted and, if so, then deactivating the defrost heater; determining whether to increase the refrigerant temperature to prevent condensation on the external surfaces of the refrigerator appliance.
 2. The method of claim 1, further comprising the step of decreasing the condenser fan speed if the refrigerant temperature is determined to be increased.
 3. The method of claim 1, further comprising the step of increasing the compressor speed if the refrigerant temperature is determined to be increased.
 4. The method of claim 1, wherein the step of determining whether to increase the refrigerant temperature comprises determining the relative magnitude of the time t_(defrost).
 5. The method of claim 1, wherein the step of determining if the evaporator is defrosted comprises monitoring a defrost termination thermostat.
 6. The method of claim 1, further comprising the steps of: waiting a time interval t_(ice) if the defrost heater is deactivated; and then reactivating the defrost heater.
 7. The method of claim 1, further comprising the step of establishing a time interval t_(ice) during the step of deactivating the defrost heater.
 8. The method of claim 7, wherein time interval t_(ice) is based at least in part on time t_(defrost).
 9. A method for operating a refrigerator appliance, the refrigerator appliance comprising a refrigeration system for cycling a refrigerant therethrough that includes a compressor, a condenser, and an evaporator, the method comprising the steps of: activating a defrost heater configured to melt ice built up on the evaporator; counting a time t_(defrost); determining if evaporator is defrosted and, if so, then deactivating the defrost heater, waiting a time interval t_(ice), and reactivating the defrost heater; determining whether to increase the refrigerant temperature to prevent condensation on the external surfaces of the refrigerator appliance.
 10. The method of claim 9, further comprising the step of decreasing the condenser fan speed if the refrigerant temperature is determined to be increased.
 11. The method of claim 9, further comprising the step of decreasing a condenser fan speed if the refrigerant temperature is determined to be increased.
 12. The method of claim 9, wherein the step of determining whether to increase the refrigerant temperature comprises determining the relative magnitude of the time t_(defrost).
 13. The method of claim 9, wherein the step of determining if the evaporator is defrosted comprises monitoring a defrost termination thermostat.
 14. The method of claim 9, further comprising the step of establishing the time interval t_(ice) during the step of deactivating the defrost heater.
 15. The method of claim 9, wherein time t_(ice) is based at least in part on time t_(defrost).
 16. A refrigerator appliance, comprising: at least one compartment for storing food items; a refrigeration system for cycling a refrigerant therethrough, the refrigeration system comprising a compressor; a condenser; a condenser fan; an evaporator; and a defrost heater configured to melt ice accumulated on the evaporator; a controller in operative communication with the compressor and the condenser fan, the controller configured for activating a defrost heater configured to melt ice built up on the evaporator; counting a time t_(defrost); determining if evaporator is defrosted and, if so, then deactivating the defrost heater; determining whether to increase the refrigerant temperature to prevent condensation on the external surfaces of the refrigerator appliance.
 17. The refrigerator appliance of claim 16, wherein the controller is further configured for decreasing the condenser fan speed if the controller determines to increase the refrigerant temperature.
 18. The refrigerator appliance of claim 16, wherein the controller is further configured for increasing the compressor speed if the controller determines to increase the refrigerant temperature.
 19. The refrigerator appliance of claim 16, wherein the controller is further configured for establishing a time interval t_(ice) during the step of deactivating the defrost heater; waiting time interval t_(ice); and reactivating the defrost heater, wherein time interval t_(ice) is based at least in part on time t defrost. 